The solubility of rare earth carboxylates may be directly related to their catalytic activity in Ziegler-Natta polymerization (homogeneous polymerization) reactions of butadiene, isoprene, and other olefins. Solubility of the solid is measured as the amount of a solid which is dissolved at a given concentration, and can be measured by the transmittance of light through the solution.
The cloudiness produced by the presence of undissolved particles in the solution is measured by the transmittance of light (about 420 nm) through the solution. If there is a quantity of solids remaining undissolved in the solution, it is difficult for light to pass through. As the solid is dissolved in the solution, more light passes through, giving a higher percent transmittance. A solid being approximately completely soluble will allow 100% transmittance of light on the maximum transmittance of light through the solvent.
Improvement of solubility can also include the ability to make more concentrated solutions of rare earth carboxylates. An object of the present invention, is to make, by dissolving the improved solid rare earth carboxylates, a more concentrated solution in comparison to concentrated solutions made by dissolving the original (commercially available) solid rare earth carboxylates.
In this invention, the preparation of powdery, solid rare earth carboxylates which are highly soluble in an aliphatic solvent is described. It is theorized that by the use of other ligands in the place of some of the carboxylate ligands, a powdery solid which is highly soluble in an aliphatic solvent and is also a highly active catalyst for the polymerization of butadiene, isoprene, and mixtures thereof is formed. Also a new method to dissolve solid rare earth carboxylates in an aliphatic solvent using carboxylic acids and other solubilizing agents is described.
Solid rare earth carboxylates with branched long-chain ligands (e.g. rare earth versatate, rare earth neodecanoate, rare earth octanoate, rare earth 2-ethyl hexanoate, rare earth naphthenate and mixtures thereof) can be produced by a variety of methods including solid-state methods, aqueous precipitation, and solvent evaporation. Improved methods including aqueous precipitation and improved solvent evaporation methods provide solid rare earth carboxylates which are powdery and free-flowing. Improved methods are described in U.S. Pat. No. 5,783,676, entitled "Synthesis of Solid, Powdery Rare Earth Carboxylates by a Precipitation Method," Ser. No. 08/623,722, issued Jul. 21, 1998, and in U.S. patent application entitled, "Preparation of Solid, Powdery Rare Earth Carboxylates by Evaporation," Ser. No. 60/040,327, both of which are incorporated herein in their entirety.
One difficulty that has been faced with solid rare earth carboxylates is that the solids are frequently not soluble in organic solvents at as high of concentration as can be obtained from the liquid form. An object of the present invention is to provide a solution to this problem.
Unless otherwise stated, all parts, ratios or percents are by weight.
As used herein, the terms "rare earth carboxylate(s)," "aliphatic solvent(s)," "carboxylic acid(s)," "rare earth salt(s)" "precursor(s)," "reagent(s)," and "solubilizing agent(s)" shall encompass the singular and plural, as well as, to encompass mixtures of the respective compounds.
As used herein, the terms "precursor(s)" and "reagent(s)" mean the components mixed, added, reacted or otherwise combined to form a composition, compound, solution or the like. For example, as used herein precursors or reagents of a carboxylate salt solution can include, but are not limited to, carboxylic acid, base and the reaction medium, e.g., water.
"Comprising" as used herein, means various components can be conjointly employed. Accordingly, the terms "consisting essentially of" and "consisting of" are embodied in the term "comprising."